Magnetic material and appliance



June 4, 192 9 1 ca. w. ELMEN 1,715,646

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MAGNETIC MATERIAL AND APPLIANCE Original Filed June 30, I926 4 Sheets-Sheet 2 June 4, 1929. I G. w. ELMEIQ 1,715,646

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by A77)? 'June 4, 1 G. w. ELMEN MAGNETIC MATERIAL AND APPLIAficE Original Filed June 30, 1926 4 Sheets-Sheet 4 mmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmE Patented June 4, 1929.

UNITED STATES PATENT OFFICE.

eusmr w.. EI.MEN,'oE LEONIA, NEw JERSEY, ASSIGNOR 'ro wEsrEnN ELECTRIC comm, INCORPORATED, on NEW YORK, N. Y., A CORPORATION on NEw YORK.

MAGNETIC MATERIAL AND APPLIA NGEL Application filed June 30, 1926, Serial No. 119,622. Renewed December 20, 1928.

This invention relates to magnetic materials or compositions and electromagnetic systems. It has wide application and is especially useful in signaling circuits. The materials of this invention possess several remarkable characteristics, among which are practically constant permeability accompanied by negligible hysteresis, remanence and coercivity for a wide range of magnetizing forces and hi h permeability with low hysteresis at big magnetlzlng forces.

As a material the invention has its embodiment in a composition containing cobalt, nickel and iron. The proportions of the ingredients and the treatment of thematerial may be varied to emphasize one or more of its characteristics.

. Iron is the material which has been almost universally used in the past for the magnetic circuits of electrical machines and apparatus,

but within recent years compositions of iron with small percentages of silicon, commonly known as silicon-iron or silicon-steel, have found extensive uses in the electrical arts.

More recently the present inventor discovered that certain compositions containing nickel'and iron as the principal ingredients can be given very high permeability at low magnetlzing forces and low hysteresis as compared with iron. See the paper by H. D. Arnold and G. W. Elmen entitled Permal- 10y, Journal of the Franklin Institute, May, 1923. See also U. S. Patents 1,586,884: and 1,586,887, issued June 1, 1926. With certain of these compositions, when properly heat treated, low variability of permeability at low magnetizing forces may be obtained, but to no such marked degree as in the present invention.

Several representative compositions are herein described and the drawings include curves pertaining to, one such composition which consists of approximately 45% nickel, 25% cobalt and 30% iron with about 0.5% manganese added to increase workability. The curves were obtained with a sample which was heat treated to develop constancy of permeability in the manner hereinafter described.

Fig. 1 is a magnetization curve for this composition.

Fig. 2 is a permeability-magnetizing force curve.

Fig. 3 shows the upper halves' of hysteresis loops for thisco'mposition, Armco iron and show. the upper at difi'erent magsuperposed a steady magnetizing force, the

amount of which is varied.

Fig. 12 is an elevation of a conductor continuously loaded with the material of this invention.

Fig. 13 is a diagrammatic illustration of a composite telephone and telegraph system containin magnetic elements in accordance with this invention.

The magnetization curve of Fig. 1 illustrates the relation between the magnetizing force H and the induced flux density B in c. g. s. units while Fig. 2 shows the variation 1n permeability with magnetizing force computed from the same data. The curve of Fig. 2 illustrates the remarkable constancy of permeability up to a magnetizing force of almost two gauss. The initial permeability, as shown in Fig. 2, is approximately 460, which is considerably higher than that of good grades of commercial iron and is approximately that of the best silicon steel. In the range from 2.5 to 4 gauss there 1s avery rapld rise in permeability, the rate of merease remaining high nearly to the point of maximum permeability, which is about 2100. Another interesting character istic of this material, as illustrated in Fig. 1 is the hi h flux density at large magnetizing forces; or example, 15,000 at a force of'45 gauss.

Fig. 3 shows the upper half of a hysteresis loopa of the 45% Ni25% 00-30% Fe composition compared with hysteresis loops Z; and c for silicon steel and Armco iron, respectively, all carried to a maximum induction of approximately 600 e. g. s. units. The two sides of thehysteresis loop a for the new magnetic material could not be distinguished from a single straight line passing through the origin, according to careful measurements made by ballistic methods, in-

dicating that no hysteresis'is present and that the coercive force and remanence are both zero. As a more sensitive method of detecting hysteresis, a Wheatstone inductance bridge method was used. It was found that the hysteresis loss at an induction of 100 c. g. s. units was .024X10' ergs per cu. em. per cycle. For practical purposes such a vanishingly small amount is negligible. The coercive force and remanence indicated by loo a are also quite negligible whereas the va ues of these quantities indicated by 100 s b and 0 are of considerable magnitude.

he hysteresis loss in a nickel-iron alloy containing 78 nickel and 21 iron,

heat-treated to develop high initialperme ability, is much less than that for silicon steel or iron. In a particular sample of such an alloy, the hysteresis loss at an induction of 100 c. g. s. units was found to be 33X 10- ergs per cu. cm. per cycle, which is over 1000 times that found for the new material.

Figs. 4 to 9, inclusive, are the upper halves of hysteresis loops of the nickel-25% cobalt-30% iron composition for various maximum inductions and show the manner of growth of the hysteresis loss with increasing induction. The curve of Fig. 4 is-from the same data as curve a of Fig. 3, the circles on this plot indicating points on the ascending branch, and the dots, points on the de-' scending branch. The dots and circles fall on a single straight line assing through the origin, indicating not on y constancy of permeability, but absence of hysteresis, remanence and coercive force. The uppermost point of this straight line corresponds to a magnetizing force of about 1.3 gauss and an induction of about 570.

Figs. 5 to8, inclusive, show the growth of the hysteresis loop as the flux density .is increased above the maximum value shown in Fig. 4. The existence of hysteresis becomes apparent in Figs. 5 and 6, for example, but the areas of the loops are comparatively small. 'The permeability begins to vary at about 1.3 gauss but the variation up to 1.7 gauss and even beyond is hardly discernable. When the flux density reaches values of 1500 or more, as shown in Figs. 7 and 8, the hysteresis loss increases rapidly, but it is to be noted that the remanence and the coercive force are still practically zero, thus giving the complete hysteresis loop a peculiar shape which has been characterized as wasp-waisted. It may be inferred from these figures that there is a definite relation between constancy of permeability and the elimination of hysteresis loss.

Fig. 9 shows the upper half of the hysteresis loop for a flux density of approximately 15,000 c. g. s. units. This loop has more nearly the general shape of the ordinary hysteresis loop obtained with iron and other magnetic materials. It difiers radi- -at this high maximum flux density 'is also small compared with that of the usual magnetlc materials. The hysteresis loss reaches a limiting value at a magnetizing forceof about 7 gauss as shown by the curve, and remains constant at higher forces.

Fig. 10 shows the magnetization curve of the virgin material up to a maximum flux density of 8500, and'the'hysteresis loop for the same maximum flux density. The curve A. indicates the'ascendin branch and curve B the descending branc of the hysteresis loop, while curve C is the magnetization curve. The relative positions of the magnetization curve C and the ascending branch A of the hysteresis loo shows an, interesting characteristic. In or inary magnetic materials, the magnetization curve is either entirely above the ascending branch of the hysteresis loop, as is generally the case, or crosses it at a relatively high value of magnetizing force, while in this case the ascending branch of the hysteresis loop rises above the magnetization curve at a very low magnetizing force and continues above up to fairly high magnetizing forces.

Fig. 11 illustrates graphically the relation of the permeability to a constant alternating current magnetizlng force of about .0021 gauss at 200 cycles per second when a steady magnetizing force is superposed on the magnetic circuit, the steady force being produced by a direct current increased in small steps. The arrows in this figure indicate the direction of the progress of the permeability as the direct current magnetizing force is varied. The permeability is substantially constant as the direct current magnetizing force increases up to approximately 1.7 gauss, and it then suddenly rises as the force is increased beyond that value. Another characteristic of this material which is not found in ordinary magnetic materials is the higher permeability at low magnetizing forces after a direct current magnetizing force of large value has been removed from the magnetic circuit. In the case shown in Fig. 11, the permeability has increased from approximately 460 to 750. It is also an interesting fact that the most careful application of the ordinary methods of demagnetization by a gradually reduced magnetic cycle fails to restore completely the permeability to the value in the virgin state. It can, however, be restored by a process of heat treatment.

The resistivity of the 45% nickel-25% cobalt30% iron composition was found to be about 19 microhm-cms.

Examples of other magnetic materials within the invention having smaller and larger percentages of cobalt respectively than the material described above will now be given. They were heat-treated to develop constancy of permeability in the manner hereinafter described.

As examples of compositions having less than 25% of cobalt may be mentioned one containing approximately 60% nickel, 15% cobalt and 25% iron, another containing approximately 70% nickel, 15% cobalt and 15% iron, and still another containing approximately 73% nickel, 6% cobalt and 21% iron. These compositions and others having a low cobalt content which were tested have the constancy of permeability of the material described above, though in general over a somewhat smaller range of magnetizing forces. Furthermore, each of these compositions, for a range of low magnetizing forces, exhibits the same ;absence of hysteresis loss, remanence and coercivity, while for somewhat larger magnetizing forces the hysteresis loss becomes appreciable although the remanence and coercivity remain negligible, and for still larger magnetizing forces the remanence, coercivity and hysteresis loss are appreciable although of comparatively small value. These compositions also, in general, have the other desirable properties of the composition containing nickel, 25% cobalt and 30% iron, but in varying degrees.

A sample of material containing nickel, 15% cobalt and 25% iron was found to have practically zero hysteresis loss up to a flux density'of about 700 e. g. s. units, and up to a magnetizing force of 1.1 ganss, with the permeability remaining constant at 631 over this range. A maximum permeability of 2680 was obtained at a magnetizing force of 2.45 gauss. At a flux density of 1520 the hysteresis loss was 88 ergs per cu. cm. per cycle, and increased with increasing flux densities, reaching 1508 ergs per cu. cm. per cycle at a flux density of 13,250 0. g. s. units and a magnetizing force of 30.7 gauss. The

, resistivity of this material was 17.5 microhm-cms.

A sample of a material containing nickel, 15% cobalt and 15% iron had substantially zero hysteresis loss up to a flux density of 320 c. g. s. units, and over a range of magnetizing forces up to 0.5 gauss, the permeability remaining constant at 390 over this range. At a flux density of 1470 c. g. s. units the hysteresis loss was 116 ergs per cu. cm. per cycle, and reached 2435 ergs-per on. cm. at a 'fiux density of 10,600 0. g. s. units. The resistivity of this material was approximately 14.25 microhm-cms.

A sample of a material containing 73% nickel, 6% cobalt and 21% iron had substantially zero hysteresis loss up to a flux density of 7150. g. s. units, and over a range of magnetizing forces from zero up to 0.5 gauss, the permeability remaining constant at 1430 over this range. A maximum permeability of 5600 was obtained at a magnetizing force of 1.1 gauss. At a flux density of 1520 c. g. s. units, the hysteresis loss was '23 ergs per cu. cm. per cycle, andv reached 783 ergs per cu. cm. per cycle at a flux density of 11,500 0. g. s. units. The resistivity of this material was approximately 15.5 microhm-cms.

Examples of materials within the invention having larger percentages of cobalt than the materials described above are, respectively, 10% nickel, 7 0% cobalt and 20% iron; and 20% nickel, 50% cobalt and 30% iron; and 30% nickel, 30% cobalt and 40% iron. These, in general, have the same characteristics as the materials already de scribed, but the constancy of permeability extends over a wider range of magnetizing forces and the permeability in this range is smaller. As in the case of the other compo sitions, hysteresis loss, remanence and coercive force are practically zero at low magnetizing forces, while for a range of slightly larger magnetizing forces the hysteresis loss becomes appreciable although the remanence and coercive force remain ractically zero, and for still larger magnetlzing forces the hysteresis loss, remanence and coercive force an; appreciable but of comparatively small va ue.

A sample of the material having 10% nickel, 70% cobalt and 20% iron had practically zero hysteresis loss up to a flux density of 225 c. g. s. units, with constancy of permeability up to the same value, the permeability being 57 over this range. The range of magnetizing force over which permeability was constant was from zero to above 4 gauss. A maximum permeability of 1545 was obtained with this material at a magnetizing force of 6.5 gauss. At a flux density of 1700 c. g. s. units the hysteresis loss was 1040 ergs per 011. cm., and at a flux density of 14,650 0. g. s. units attained with a magnetizing force of 50 gauss, was 14,160 ergs per cu. cm. The resistivity of this material was 15.38 microhm-cms.

A sample of the composition containing 20% nickel, 50% cobalt and 30% iron had a permeability of 98 from zero flux density to 400 c. g. s. units and, therefore, from zero magnetizing force to about 4 gauss. A maximum permeability of 1180 was obtained with this material at a magnetizing force of 8.3 gauss. At a flux density of 1025 c. g. s. units the hysteresis loss was 299 ergs per cu. cm., and reached 12,460 ergs per cu.

cm. at a flux density of 15,200 c. g. s. units and a magnetizing force of 50 gauss. The resistivity of this sample was 16.59

microhm-cms.

A sample of the compositlon contannng 30% nickel, 30% cobalt and 40% iron, had a permeability of 755 at zero flux density and zero magnetizing force, and was found to have 0.4% increase in permeability at a magnetizing force of 0.1413 gauss. With this composition, a maximum permeability of 2870 was obtained at a magnetizing force of 3.65 gauss. At a flux density of 4900 c. g. s. units and a magnetizing force of 50 gauss, the hysteresis loss was 1051 ergs per cu. cm. per cycle. crohm-cms. Other compositions tested having a high cobalt content had, in general, the properties of the compositions described above, but in varying degree.

The eifect of adding a small amount of chromium to a composition such as described above has been investigated. The resistivity was found to be somewhat greater but the magnetic characteristics, in general, were not greatly affected.

The magnetic properties of the materials of this invention are subject to change under the influence of mechanical strains and consequently due precautions must be taken in their utilization to avoid excessive strains and stresses.

The method of preparing one of the compositions and heat treating it will now be described, the composition being that first described above, containing 4570' nickel, 25% cobalt and 30% iron. This method is suitable for any of the compositions.

Good commercial grades of the materials to be used were fused together in a furnace and the molten composition poured into a mold to form a thick rod. The rod as taken from the mold was subjected to repeated swaging and annealing operations by which it was reduced in diameter and correspondingly elongated. The long rod thus formed was then drawn out by repeated drawing and annealing operations to a fine gauge wire and formed into a thin tape 0.125 inches wide and 0.006 inches thick by passing it between flattening rolls.

The material, having thus been prepared in the form of tape was Wound on a mandrel about 2 inches in diameter so as to form a loosely wound flat spiral ring of about forty turns. The ring thus prepared had an inner diameter of about 2% inches, an outer diameter of about 3 inches and a thickness of inch. This'ring was then placed in an annealing pot and, after the usual precautions were taken to prevent oxidation during heat-treatment, was heated in an electric furnace to a temperature around 1100 C. and was maintained at that temperature for about one hour. The furnace with the annealing pot therein was then allowed to cool to about C. before removing the ring. This cooling required approximately 16 hours. Measurements with a thermocouple in contact with the annealing pot indicated that about 3 hours The resistivity was 24.42 n1i' .1100 C. to 350 C.

Experiments with other methods of heattreatment have been made as, for example,-

one involving rapid cooling of the material and also one involving slow cooling to the magnetic transformation point followed by cooling at a more rapid rate such as would develop high permeability in certain nickeliron alloys. The latter method of heattreatment is described in the above mentioned paper by H. D. Arnold and G. W. Elmen.

The results obtained with various heat treatments indicate that the magnetic properties herein described are affected materially by the method of heat-treatment and especially by the rate of cooling. Tests indicate that the method of treatment according to which the material is cooled slowly, as by being allowed to cool in the annealing pots, gives the material the most nearly constant permeability and lowest hysteresis loss over wide ranges of flux those having a high nickel contentbut in, general wlth increase of hysteresls loss atlow field strength and at the expense of constancy of permeability. Intermediate results may be obtained by cooling at rates intermediate those described above.

As pointed out above, the improved magnetic materials of this invention are useful for many purposes. They are particularly suited for use in the magnetic circuits of signaling systems in which distortion of the wave form of signaling currents due. to variation of magnetic properties is objectionable. Such distortion is variously characterized as magnetic modulation, flutter effect, etc., depending upon the conditions under which it is produced. The materials of this invention, because of their remarkable properties of constancy of permeability and negligibly small hysteresis loss, nearly or quite eliminate such distortio Certain of the materials of the invention have very high permeability and low hysteresis loss at large magnetizing forces of the order of 30 to 40 gauss, as stated above. They are therefore very well adapted for electromagnetic devices employing large field strengths such as used in power generation and distribution.

Fig. 12 illustrates a signaling conductor continuously loaded with tape composed of the material of this invention. This conductor comprises a cylindrical copper conductor 15 having nickel-cobalt-iron tape 16 loosely wrapped thereon in the form of a helix. In some cases a second layer of loading tape 17 may be applied to the conductor,

as is done, for example, in U. S. Patent No. 1,586,884, to G. W. Elmen, issued June 1, 1926. Y

A loaded conductor of the form shown in Fig. 12 has been heat-treated as follows: A coil of the loaded conductor was placed in an annealing pot of an electric furnace and the. temperature raised to about 900 C. and maintained "there for approximately one hour. The pot was then allowed to cool down to room temperature within the furnace in the manner above described. I

In accordance'with an alternative method of heat-treating the loaded conductor, it may be .drawn lengthwise through a furnaceof the type described in. U. S. -Patent to G. W..Elmen, No. 1,586,884, issued June 1, 1926. This is an electric furnace having a horizontal iron tube with a copper lining extending therethrough and projecting beyond, the inside diameter being somewhat larger than the outside diameter of the load ed conductor. The form of furnace which it is preferred to use when a very slow rate of cooling is employed, is one in which the iron tube projects a considerable distance beyond the wall of the furnace in such manner that the heated conductor passes through the projecting portion before it passes into the air. As the loaded conductor passes from the furnace it cools first in the. air within the projecting portion of the iron tube and later in the air outside the tube which is'kept at about ordinary room temperature, 20 C.

Fig. 13 shows a composite telephone and telegraph system in which the several different magnetic elements in various parts of the system may be constructed of materials in accordance with this invention. This is a standard system of the type disclosed in Patent No. 1,530,482, to G. C. Cummings, I issued March 24, 1925, and includes a pair of line conductors L and L which have associated therewith both telegraph and telephone equipment, thereby permitting simultaneous telegraphic and telephonic communication thereover.

The apparatus which may employ the new magnetic compositions as the core material are the loading coil 24, the battery supply repeating coil 25, the phantom repeating coil 26, the relays 27 employed in the two telegraph circuits, and the coils 28 employed in the composite set. By employing the new magnetic material for the magnetic cores in such apparatus, the transmission characteristics of the circuits may be greatly improved.

A composition which has been found particularly satisfactory for the coil 24 is that containing 45% nickel, 25% cobalt and 30% iron. The limiting condition heretofore encountered in the design of such coils is the effect the telegraph current has on the transmission characteristics of the tele hone circuit when the lines are used simu taneously for telegraphing and tele honing. This effect, which appears as a cliange in the transmission characteristics of the line, is ordinar- 11y referred to as the flutter effect, and is caused by the variation of the effective resistance and the inductance of'the coils due to the change in magnetization of the magnetic material. The coil 24 may be in the form of compressed powder or may be built up of laminations in the well known manner. In a representative case in which the composition just mentioned was used as the core material the flutter was less than 1/100 that obtained with cores of compressed iron powder. In fact, with the ordinary currentyalues employed no flutter at all could be detected.

'A possible explanation of the'peculiar behavior of the new magnetic materials when heat-treated tobring out the characteristics discussed above, is that each is composed of two or more magnetic materials of very different magnetic characteristics, which materials are intimately mixed in such away that the magnetic path formed by them can be considered equivalent to a series-parallel arrangement of the two magnetic materials. This theory seems to be borne out to some extent at least by the results of tests made with magnetic cores of two magnetic materials having widely different characteristics arranged in series-parallel relation, hysteresis loops somewhat similar to that shown in Fig. 6 having been obtained by this method. 1

The appended claims are directed to certain species only of the more generic invention, described herein and described and claimed broadly in applicants copending application, Serial No. 119,622 filed of even date herewith.

What is claimed is:

1. A magnetic material containing as essential constituents thereof, nickel, cobalt and iron in which the nickel content is between 65 and 80% of the total nickel-cobaltiron content. I

2. A magnetic material containing as essential constituents thereof, nickel, cobalt and iron in which the nickel content is between to of the total nickel-cobalt-iron content.

3. A magnetic material containing as essential constituents thereof, nickel, cobalt and iron in which the cobalt content is between 4 and 14% of the total nickel-cobaltiron content.

4. A magnetic material containing as essential constituents thereof, nickel, cobalt and iron in which the nickel content is between 70 and 75% and the cobalt content is between 5 and 15% of the total nickel-cobaltiron content.

5. A magnetic material having negligible variation in permeability over a wide range of flux densities comprising nickel from 65 to 85%, cobalt 5 to 20% and the balance chiefly iron.

6. A magnetic material having negligible variation in permeability over a wide range of flux densities comprising nickel, cobal and iron as essential constituents thereof in approximate proportions of 73%, 6% and 21% respectively.

7. A magnetic composition in accordance with claim 5 having negligible hysteresis loss for flux densities up to 715 c. g. s. units.

8. A magnetic composition in accordance with claim 5 having negligible variation in permeability for magnetizing forces up to .5 gauss.

9. A magnetic composition in accordance with claim 5 characterized in this that it constitutes at least part of a magnetic circuit associated with an electrical conductor carrying a current efi'ective to set up therein a flux density less than 100 c. s. units.

10. A magnetic composition including as essential elements iron, nickel, and cobalt and includin nickel to the extent of between 65 to 85% o the iron-nickel-cobalt content, characterized by initial permeability of 800 or more and constancy of permeability within a few per cent up to a magnetizing force of at least H=.2 c. g. s. units.

11. A magnetic composition comprising 65 to 85% nickel and caused to have, by, the addition of suitable alloyin'gelements and heat treatment, an initial permeability of 800 or more, and a constancy of permeability within a few per cent up to a magnetizing force of at least .2 c. g. s. units.

In witness whereof, I hereunto subscribe day of June A. D., 1926.

my name this 29 GUSTAF- W. ELMEN. 

